Technical Field
The present disclosure relates to a webbing take-up device and a seatbelt device employing the webbing take-up device.
Related Art
Vehicles such as passenger vehicles are attached with seatbelt devices that use webbing to restrain an occupant sitting in a seat. Seatbelt devices are provided with a webbing take-up device that takes up and stores the webbing on a spool when not being worn. In webbing take-up devices, there is demand for a pre-tensioner function that restrains the occupant with the webbing in the event of sudden vehicle deceleration, in addition to a take-up function to take up the webbing onto the spool when the occupant releases wearing of the webbing.
Webbing take-up devices include what are known as “motor retractors”, in which the spool is rotated in a webbing take-up direction by drive force of a motor to take up and store the webbing. Webbing take-up devices have been proposed that include both a take-up assist mechanism to achieve a take-up function using drive force of a motor, and a pre-tensioner mechanism to achieve a pre-tensioner function (for example, Japanese Patent Application Laid-Open (JP-A) No. 2007-099257).
In JP-A No. 2007-099257, the rotation speed of an output shaft of the motor is set with at least two speeds, namely a first speed, and a second speed that is faster than the first speed. Moreover, in JP-A No. 2007-099257, a first drive force transmission mechanism that transmits rotation of the output shaft of the motor to the spool at a predetermined speed reduction ratio, and a second drive force transmission mechanism that transmits rotation of the output shaft of the motor to the spool at a higher speed reduction ratio than the predetermined speed reduction ratio, are provided as drive force transmission mechanisms.
Accordingly, in JP-A No. 2007-099257, rotation of the motor at the first speed is transmitted to the spool through the first drive force transmission mechanism such that the spool is rotated at a high speed and low torque and reliably takes up the webbing onto the spool. Moreover, in JP-A No. 2007-099257, in the event of sudden vehicle deceleration, rotation force of the motor rotated at the second speed is transmitted to the spool through the second drive force transmission mechanism such that the spool is rotated at a low speed and high torque, obtaining an occupant restraint state in response to the sudden vehicle deceleration. Moreover, JP-A No. 2007-099257 enables the webbing to be pulled out by driving the motor in reverse after the occupant restraint state in the event of sudden vehicle deceleration in order to release the locked state of the spool.
Note that under normal circumstances, webbing take-up includes take-up to place the webbing in firm contact with the occupant when the occupant is wearing the webbing, and take-up to store the webbing when wearing has been released. To take up the webbing when wearing has been released, it is necessary to lower the take-up torque of the spool, so as to achieve take up with trouble-free movement of the webbing and tongue provided to the webbing.
However, when taking up the webbing to place the webbing in firm contact with the occupant, it is necessary to pull the webbing tightly to place the webbing in firm contact with the occupant in order to remove any slight looseness, known as “slack”, in the webbing worn by the occupant. However, if the webbing is pulled too tightly, a large load is placed on the shoulder region of the occupant, for example, causing the occupant discomfort. Accordingly, in order to place the webbing in firm contact with the occupant, it is necessary to set the take-up torque of the spool so as to obtain an appropriate occupant restraint performance without placing a larger load on the occupant than is necessary.
In webbing take-up devices employing a motor, the take-up function demands reliable slack removal in order to secure high occupant restraint performance in a state in which the webbing is being worn. Moreover, for take up functionality, when webbing released from wearing by the occupant is taken up onto the spool, there is demand for smooth take up at a lower take-up torque than the take-up torque when placing the webbing in firm contact with the occupant.